1. Field of the Invention
The present invention relates to improvements in two-stroke cycle internal combustion engines suitable for automotive, marine, and stationary power.
2. Description of the Prior Art
Two-stroke cycle spark-ignition engines have long found commercial success in applications other than heavy automobile propulsion. They were previously employed in very light economy cars, motorcycles, and small service vehicles. The two-stroke engine was used as an automobile power plant in Europe but was abandoned by Saab and Auto Union by the late 1960's. The Japanese continued using the two-stroke until the end of the 1970's. The two-stroke is currently used in eastern Germany for economy cars.
The automotive two-stroke engines disappeared because they did not fulfill emission control standards. Additionally, the prior art designs consumed more fuel and ran rougher than their four-stroke counterparts. The two-stroke produced dirty exhaust partly because of the necessity of mixing large amounts of oil with the fuel to obtain crank lubrication.
The limited application of the two-stroke isolated it from heavy development, as well as most of the advances in the combustion arts, for the past two decades.
Intense interest in the two-stroke for automotive application is on the rise. General Motors, Ford, Chrysler, and Japan are involved in two-stroke projects. It is reported that Chrysler will have a high-performance two-stroke V-6 passenger car in production by 1997. General Motors is investing in an engine design proposed by Orbital Engine Co. of Australia.
Some analysts and engineers predict that if industrial and scientific might is intelligently focused on the two-stroke it will signal the beginning of a new era in automotive propulsion.
The potential benefits of two-stroke engines are its simplicity, light weight, and a power stroke in each cylinder during each revolution of the crankshaft.
The relatively small size of the two-stroke engine can produce low hood lines in road automobiles, which have an aerodynamic as well as aesthetic value.
The two-stroke offers the potential of large power outputs per unit of engine displacement. It is well known by motorcycle engineers that racing two-strokes have exceeded specific outputs of 400 horsepower per liter. Also, marine outboard motors of high power to weight ratios are commercially available as stock items.
Very well designed prior art two-stroke spark ignition engines attained 90 percent of the gasoline mileage of well designed four-stroke counterparts. A portion of the poorer gasoline mileage and dirty exhaust is due to the exhaust port remaining open during the scavenging process, thereby allowing leakage of fresh mixture out the exhaust system. Another portion of the poor mileage and dirty exhaust is due to spurious misfires or pre-ignition at light loads, which is poorly understood because of limited investigation.
With the development of computer controlled engine management and direct fuel injection, the dirty exhaust, rough running, and mileage limitations of the prior art two-stroke designs can be removed, because the air to fuel ratio and spark timing can be monitored and controlled in realtime, throughout the engine's speed range, in harmony with its instantaneous load.